1. Field of the Invention
The present invention relates to an IC card and, more particularly, to a non-contact type IC card having a microcomputer incorporating a data memory, a battery and other built-in components.
2. Description of the Related Art
In recent years, non-contact type IC cards have been developed which have various built-in components such as a data processing CPU, a data memory for storing data, a transmission/receiving device for exchange of data with external devices, a battery for supplying power to internal circuits, and so forth. It is desirable that this type of IC card have a voltage detection circuit for detecting a reduction in the voltage of the built-in battery.
A voltage detection circuit for this purpose is already known. This known circuit has a Zener diode for generating a reference voltage by using the power of the built-in battery, a resistor for dividing the potential or output voltage of the battery, and means for comparing the measured divided voltage with the reference voltage so as to produce a signal when the measured voltage has become lower than the reference voltage.
This known voltage detection circuit, however, has suffered from a problem in that different circuits have different levels of voltage detection so that the accuracy of the voltage detection is not so high, due to fluctuations in the properties of the components such as the Zener diode and the voltage-dividing resistor.